1. Field of the Invention:
The present invention relates to a sensor comprising a field-effect transistor (FET) as a pressure-sensitive element for detecting a physical quantity such as pressure, acceleration, etc., and more particularly to a semiconductor sensor capable of producing a detected output signal which has been temperature-compensated.
2. Relevant Art:
There is known one type of semiconductor sensor which comprises a pressure-sensitive element in the form of an FET whose drain current varies when it is put under pressure, strain, or the like. The semiconductor sensor is associated with a temperature compensating circuit which compensates for a temperature-dependent change in the drain current. The temperature compensating circuit may comprise a temperature-detecting FET, and output signals from the pressure-detecting FET and the temperature-detecting FET may be compared with each other for temperature compensation. Such an arrangement however results in an increased semiconductor chip area of the semiconductor sensor.
Japanese Laid-Open Patent Publication No. 58(1983)-015029 and Japanese Patent Publication No. 1(1989)-59525 disclose a scheme for temperature compensation without use of a temperature-detecting FET. In the disclosed arrangement, the gate bias voltage of the pressure-detecting FET is set to a value which makes the temperature dependency on the VGS-IDS characteristic curve substantially null.
The sensitivity of an FET for detecting a physical quantity applied thereto, i.e., a change in the drain current which is caused by a change in the physical quantity applied thereto, depends on the value of the drain current. If the gate bias current of the FET is set to a value that makes the temperature dependency substantially null, then a desired degree of detecting sensitivity may not be achieved. Different FET characteristics require different gate bias voltages and different drain currents, necessitating adjustments of the circuit for applying the gate bias voltage and the circuit for amplifying output signals.